Feedback control system for polymer modification of toner resins and toners

ABSTRACT

An apparatus for the preparation of a mixture of toner resin and initiator, to form a toner resin or toner mixture including cross-linked microgel particles is provided. The apparatus includes a toner extruder having the resin being conveyed therethrough and an adder for adding the initiator to the toner resin in the toner extruder to form the toner resin or mixture. The apparatus also includes a measurer for measuring the cross-linked microgel particles in the toner mixture substantially immediately after mixing in the toner extruder and transmitting a signal indicative of the quantity of cross-linked microgel particles in the toner resin or mixture. The apparatus also includes a controller for controlling the addition rate of initiator in response to the signals from the measurer.

The present invention relates to a method and apparatus formanufacturing resins. More particularly, invention relates to anapparatus and method for chemically modifying resins.

In the process of electrophotographic printing, a photoconductivesurface has an electrostatic latent image recorded therein. Tonerparticles are attracted from carrier granules to the latent image todevelop the latent image. Thereafter, the toner image is transferredfrom the photoconductive surface to a sheet and fused thereto.

Typically, toner may be produced by melt-mixing the soft polymer andpigment whereby the pigment is dispersed in the polymer. The polymerhaving the colorant dispersed therein is then pulverized. Recently inU.S. Pat. No. 5,227,460 (Mahabadi et al.), incorporated herein byreference, a low melt toner resin with minimum fix temperature and widefusing latitude containing a linear portion and a cross-linked portioncontaining high density cross-linked microgel particles, butsubstantially no low density cross linked polymer was disclosed. Amethod of manufacturing that toner and its resin was disclosed in U.S.Pat. No. 5,376,494 (Mahabadi et al.), incorporated herein by reference.The method of fabricating the low fix temperature toner resins includesa reactive melt mixing process wherein polymer resins are cross-linkedat high temperature and high shear. The resins are particularly suitablefor high speed fusing, show excellent offset resistance and wide fusinglatitude and superior vinyl offset properties. Measurement of the gelcontent of the toner extruded in the manufacture of the toner takesapproximately 36 to 72 hours, prohibiting the use of real time feedbackand subobtimizing the control of the gel content in these toner resins.

The following disclosures may be relevant to various aspects of thepresent invention:

U.S. Pat. No. 5,145,762 Patentee: Grushkin Issue Date: Sep. 8, 1992

U.S. Pat. No. 4,973,439 Patentee: Chang et al. Issue Date: Nov. 27, 1990

U.S. Pat. No. 4,894,308 Patentee: Mahabadi et al. Issue Date: Jan. 16,1990

U.S. Pat. No. 3,778,287 Patentee: Stansfield et al. Issue Date: Dec. 11,1973

U.S. Pat. No. 5,227,460 Patentee: Mahabad, et al. Issue Date: Jul. 13,1993

U.S. Pat. No. 5,376,494 Patentee: Mahabadi et al. Issue Date: Dec. 27,1994

U.S. patent application No. 08/247,821 Applicants: Proper et al. FilingDate: May 23, 1994

The relevant portions of the foregoing disclosures may be brieflysummarized as follows:

U.S. Pat. No. 5,145,762 (Grushkin) discloses a process for thepreparation of toner compositions. The process comprises melt blendingtoner resin particles, magnetic particles, wax, and charge additives.The process further comprises adding a coupling component to theaforementioned mixture, injecting water therein, and cooling.

U.S. Pat. No. 4,973,439 (Chang at al.) discloses an apparatus forobtaining toner particles with improved dispersion of additivecomponents therein comprised of a toner extrusion device containingtherein a blending chamber, a mixing screw, a heater, a toner supply,and an injector for injecting additive components including chargecontrol agents into the extrusion device enabling a decrease in themelting temperature of the toner resin particles contained therein.

In U.S. Pat. No. 4,894,308 (Mahabadi et al.), a process for preparing anelectrophotographic toner is disclosed which comprises premixing andextruding a pigment, a charge control additive and a resin. The pigmentand the charge control additive may be premixed prior to being added tothe extruder with the resin; alternatively, the pigment and chargecontrol additive may be premixed by adding them to the extruder via anupstream supply means and extruding them, and subsequently adding theresin to the extruder via a downstream supply means.

In U.S. Pat. No. 3,778,287 (Stansfield et al.) dispersions of inorganicpigments, lakes or toners in organic liquids containing polyestersdissolved therein having acid values up to 100 derived from certainhydroxy-containing, saturated or unsaturated aliphatic carboxylic acidsare described. While liquid colorants offer the distinct advantage ofbeing more readily incorporated into the medium to be colored than drypigments, their commercial significance is seriously limited due to theproblems of handling and storing potentially hazardous liquid chemicals.Thus, from an economic and safety standpoint, it is desirable to havethe colorants in a dry, storage stable form which is readily dispersiblein a wide variety of coating media without detriment to any of thedesirable properties of coating produced therefrom.

U.S. Pat. No. 5,227,460 (Mahabadi et al.) discloses a low melt tonerresin with minimum fix temperature and wide fusing latitude containing alinear portion and a cross-linked portion containing high densitycross-linked microgel particles, but substantially no low density crosslinked polymer.

U.S. Pat. No. 5,376,494 (Mahabadi et al.) discloses a method offabricating low fix temperature toner resins by a reactive melt mixingprocess wherein polymer resins are cross-linked at high temperature andhigh shear. The resins are particularly suitable for high speed fusing,show excellent offset resistance and wide fusing latitude and superiorvinyl offset properties.

U.S. patent application No. 08/247,821 (Proper et al.) discloses anapparatus for the preparation of a mixture of toner resin and a liquidcolorant. The apparatus includes a toner extruder having the resin beingconveyed therethrough and a colorant feeder for adding the colorant tothe toner resin in the toner extruder to form the toner mixture. Thecolor of the extrudate is measured, compared to a standard and theamount of colorant added is modified accordingly.

In accordance with one aspect of the present invention, there isprovided an apparatus for the preparation of a mixture of toner resinand initiator, to form a modified resin or toner mixture includingcross-linked microgel particles. The apparatus includes a toner extruderhaving the resin being conveyed therethrough and a feeder for adding theinitiator to the toner resin in the toner extruder to form the tonermixture. The apparatus also includes a measurer for measuring thecrosslinked microgel particles in the toner mixture substantiallyimmediately after mixing in the toner extruder and transmitting a signalindicative of the quantity of crosslinked microgel particles in thetoner mixture.

In accordance with another aspect of the present invention, there isprovided a method for the preparation of toner compositions includingcrosslinked microgel particles from a mixture of toner resin and aninitiator. The method includes the steps of conveying the resin throughan extruder, adding the initiator to the toner resin in the extruder toform the toner mixture, measuring the crosslinked gel in the tonermixture substantially immediately after mixing in the toner extruder,and transmitting a signal indicative of the quantity of cross-linkedmicrogel particles in the toner mixture.

In accordance with yet another aspect of the present invention, there isprovided a method for the preparation of toner compositions includingcross-linked microgel particles from a mixture of toner resin and aninitiator. The method includes the steps of conveying the toner resinthrough an extruder, adding the initiator to the toner resin in theextruder to form the toner mixture, measuring spectral bands of thecross-linked gel in the toner, converting the spectral bands into ameasurement of the cross-linked gel, and transmitting a signalindicative of the quantity of cross-linked microgel particles in thetoner mixture.

The invention will be described in detail herein with reference to thefollowing Figures in which like reference numerals denote like elementsand wherein:

BRIEF DISCRIPTION OF DRAWINGS

FIG. 1 is a schematic elevational view of an extruder utilizing thechemical initiator addition system of the present invention;

FIG. 2 is a block diagram of the chemical initiator injection system ofFIG. 1;

FIG. 3 is a graph of the near-infrared measured gel content and thegravimetric measured gel content for a toner resin utilized in thepresent invention; and

FIG. 4 is a graph of the % transmission of light and the wavelength fora toner resin utilized in the present invention.

According to the present invention, the toner created by the process ofthis invention comprises a resin and preferably a charge controladditive and other known additives. The manufacture of black toners willbe discussed henceforth. It should be readily apparent that themanufacture of colored toner may likewise include the process of thepresent invention.

The base resin used in the process of this invention is a reactivepolymer, preferably a linear reactive polymer such as, for example,linear unsaturated polyester. In preferred embodiments, the base resinhas a degree of unsaturation of about 0.1 to about 30 mole percent,preferably about 5 to about 25 mole percent. In a preferred embodiment,the linear unsaturated polyester base resin is characterized bynumber-average molecular weight (Mn) as measured by gel permeationchromatography (GPC) in the range typically from 1000 to about 20,000,and preferably from about 2000 to about 5000, weight-average molecularweight (M_(w)) in the range typically from 2000 to about 40,000, andpreferably from about 4000 to about 15,000. The molecular weightdistribution (M_(w) /M_(n)) is in the range typically from about 1.5 toabout 6, and preferably from about 2 to about 4. Onset glass transitiontemperature (T_(g)) as measured by differential scanning calorimetry(DSC) is in the range typically from 50° C. to about 70° C., andpreferably from about 51° C. to about 60° C. Melt viscosity as measuredwith a mechanical spectrometer at 10 radians per second is from about5,000 to about 200,000 poise, and preferably from about 20,000 to about100,000 poise, at 100° C. and drops sharply with increasing temperatureto from about 100 to about 5000 poise, and preferably from about 400 toabout 2,000 poise, as temperature rises from 100° C. to 130° C.

Linear unsaturated polyesters used as the base resin are low molecularweight condensation polymers which may be formed by the step-wisereactions between both saturated and unsaturated diacids (or anhydrides)and dihydric alcohols (glycols or diols). The resulting unsaturatedpolyesters are reactive (e.g., cross-linkable) on two fronts: (i)unsaturation sites (double bonds) along the polyester chain, and (ii)functional groups such as carboxyl, hydroxy, etc. groups amenable toacid-base reactions. Typical unsaturated polyesters useful for thisinvention are prepared by melt polycondensation or other polymerizationprocesses using diacids and/or anhydrides and diols. Suitable diacidsand anhydrides include but are not limited to saturated diacids and/oranhydrides such as, for example, succinic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid,isophthalic acid, terephthalic acid, hexachloroendomethylenetetrahydrophthalic acid, phthalic anhydride, chlorendic anhydride,tetrahydrophthalic anhydride, hexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, tetrachlorophthalic anhydride,tetrabromophthalic anhydride, and the like and mixtures thereof; andunsaturated diacids and/or anhydrides such as, for example, maleic acid,fumaric acid, chloromaleic acid, methacrylic acid, acrylic acid,itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, andthe like and mixtures thereof. Suitable diols include but are notlimited to, for example propylene glycol, ethylene glycol, diethyleneglycol, neopentyl glycol, dipropylene glycol, dibromoneopentyl glycol,propoxylated bisphenol-A, 2,2,4-trimethylpentane-1,3-diol, tetrabromobisphenol dipropoxy ether, 1,4-butanediol, and the like and mixturesthereof, soluble in good solvents such as, for example, tetrahydrofuran,toluene and the like.

Preferred linear unsaturated polyester base resins are prepared fromdiacids and/or anhydrides such as, for example maleic anhydride, fumaricacid, and the like and mixtures thereof, and diols such as, for example,propoxylated bisphenol-A, propylene glycol, and the like and mixturesthereof. A particularly preferred polyester is poly(propoxylatedbisphenol A fumarate).

Substantially any suitable unsaturated polyester can be used in theprocess of the invention, including unsaturated polyesters known for usein toner resins and including unsaturated polyesters whose propertiespreviously made them undesirable or unsuitable for use as toner resins(but which adverse properties are eliminated or reduced by cross-linkingthem by the process of the present invention).

In a process of this invention, a reactive base resin and a chemicalinitiator are fed to a reactive melt mixing apparatus and cross-linkingis carried out at high temperature and high shear to produce across-linked resin which enables the preparation of low fix temperaturetoners with good fusing latitude and vinyl offset properties.

Any appropriate initiation technique for cross-linking can be used inthe process of the invention. Chemical initiators such as, for example,organic peroxides or azo-compounds are preferred for this process.Suitable organic peroxides include diacyl peroxides such as, forexample, decanoyl peroxide, lauroyl peroxide and benzoyl peroxide,ketone peroxides such as, for example, cyclohexanone peroxide and methylethyl ketone, alkyl peroxyesters such as, for example, t-butyl peroxyneodecanoate, 2,5-dimethyl 2,5-di (2-ethyl hexanoyl peroxy) hexane,t-amyl peroxy 2-ethyl hexanoate, t-butyl peroxy 2-ethyl hexanoate,t-butyl peroxy acetate, t-amyl peroxy acetate, t-butyl peroxy benzoate,t-amyl peroxy benzoate, oo-t-butyl o-isopropyl mono peroxy carbonate,2,5-dimethyl 2,5-di (benzoyl peroxy) hexane, oo-t-butyl o-(2-ethylhexyl) mono peroxy carbonate, and oo-t-amyl o-(2-ethyl hexyl) monoperoxy carbonate, alkyl peroxides such as, for example, dicumylperoxide, 2,5-dimethyl 2,5-di (t-butyl peroxy) hexane, t-butyl cumylperoxide, α-α-bis (t-butyl peroxy) diisopropyl benzene, di-t-butylperoxide and 2,5-dimethyl 2,5-di (t-butyl peroxy) hexyne-3, alkylhydroperoxides such as, for example, 2,5-dihydro peroxy 2,5-dimethylhexane, cumene hydroperoxide, t-butyl hydroperoxide and t-amylhydroperoxide, and alkyl peroxyketals such as, for example, n-butyl4,4-di (t-butyl peroxy) valerate, 1,1-di (t-butyl peroxy)3,3,5-trimethyl cyclohexane, 1,1-di (t-butyl peroxy) cyclohexane, 1,1-di(t-amyl peroxy) cyclohexane, 2,2-di (t-butyl peroxy) butane, ethyl3,3-di (t-butyl peroxy) butyrate and ethyl 3,3-di (t-amyl peroxy)butyrate. Suitable azo-compounds include azobis-isobutyronitrile,2,2'-azobis (isobutyronitrile), 2,2'-azobis (2,4-dimethylvaleronitrile), 2,2'-azobis (methyl butyronitrile), 1,1'-azobis (cyanocydohexane) and other similar known compounds.

In the cross-linking reaction which occurs in the process of the presentinvention at high temperature and high shear, the chemical initiator,such as for example benzoyl peroxide, dissociates to form free radicalswhich attack the linear unsaturated base resin polymer chains (e.g., atdouble bonds) to form polymeric radicals. Cross-linking occurs as thesepolymeric radicals react with other unsaturated chains or otherpolymeric radicals many times, forming very high molecular weight gelparticles with high cross-linking density.

The cross-linking which occurs in the process controlled by the presentinvention is characterized by at least one reactive site (e.g., oneunsaturation) within a polymer chain reacting substantially directly(e.g., with no intervening monomer(s)) with at least one reactive sitewithin a second polymer chain, and by this reaction occurring repeatedlyto form a series of cross-linked units. This polymer cross-linkingreaction may occur by a number of mechanisms.

This manner of cross-linking between chains will produce a large, highmolecular weight molecule, ultimately forming a gel.

A small concentration of initiator is adequate to carry out thecross-linking, usually in the range from about 0.01 to about 10 percentby weight of initiator in the base resin, and preferably in the rangefrom about 0.1 to about 4 percent by weight of initiator in the baseresin. By carrying out the cross-linking in the melt state at hightemperature and high shear in a melt mixing device such as an extruder,the gel particles formed during cross-linking are kept small (i.e. lessthan about 0.1 micron, and preferably about 0.005 to about 0.1 micron,in average volume particle diameter as determined by scanning electronmicroscopy and transmission electron microscopy) and their size does notgrow with increasing degree of cross-linking. Also, the high shearenables the microgel particles to be substantially uniformly dispersedin the polymer melt.

An advantage of using a chemical initiator as the cross-linking agent isthat by utilizing low concentrations of initiator (for example, lessthan 10 percent by weight and often less than 4 percent by weight) andcarrying out the cross-linking at high temperature, little or nounreacted initiator remains in the product, and therefore, the residualcontaminants produced in the cross-linking reaction are minimal.

Thus, the cross-linked resin produced in the process controlled by thisinvention is a clean and safe polymer mixture comprising cross-linkedgel particles and a noncross-linked or linear portion but substantiallyno sol. The gel content of the cross-linked resin ranges from about0.001 to about 50 percent by weight, and preferably from about 0.1 toabout 40 or 10 to 19 percent by weight

The resin or resins are generally present in the resin-toner mixture inan amount of from about 50 percent to about 100 percent by weight of thetoner composition, and preferably from about 80 percent to about 100percent by weight.

Additional components of the toner may be added to the resin prior tomixing the resin with the chemical initiator. Alternatively, thesecomponents may be added during extrusion. Some of the additionalcomponents may be added after extrusion, such as the charge controladditives, particularly when the toner is to be used in a liquiddeveloper. These components include but are not limited to stabilizers,waxes, and charge control additives. The present invention enables themeasurement and control of these components via the feedback controlloop.

The conventional measurement or assay for the extent of thecross-linking in reactive extrusion of unsaturated polyester resins isthe wet-chemical gravimetric analysis for insoluble gel. This analysisrequires a minimum of 36 hours, and offers no possibility, therefore,for rapid-turnaround or on-line analysis.

The percent transmission of light through a resin sample in the nearinfrared wavelength range (1100-2400 nanometers) varies with the gelcontent in at least three spectral bands, namely at around 1180nanometers (nm), 1660 nm and 2250 nm. This information is showngraphically in FIG. 5.

The percent transmission of light through a resin sample at threespectral bands, namely at around 1180 nm, 1660 nm and 2250 nm isproportional to the quantity of cross-linked polyester in the resincomposition exiting an extruder. A comparison of the wet-chemicalgravimetric analysis for insoluble gel was made to the spectrum fromeach scan of a near infrared (NIR) spectrophotometer on a resin samplewith an interactance probe installed in the die head of the extruder.Partial Least Squares (PLS) regression modeling was used to build acalibration equation between the percent transmission of light atspectral bands around 1180 nm, 1660 nm and 2250 nm to the gel content inthe sample.

To validate this model, gravimetric gel measurements were made andcompared with NIR measurements taken during polyester cross-linking runsof extruded resin. Table 2 is a listing of the 25 resin samples ofextruded resin for which gravimetric gel measurements were comparedagainst PLS regression derived gel content from NIR spectral bands. Theresults were used to build a calibration equation for on-linemeasurement. Four distinct levels of gel content were used: 2%, 6%, 11%,and 30%.

Results of this analysis is shown in Table 1 as follows:

                  TABLE 1                                                         ______________________________________                                                    Gravimetric Measured                                                                         NIR Measured                                       Resin ID    % Gel          % Gel                                              ______________________________________                                        REX01-10G   8              7.496                                              REX01-10G   8.2            8.92                                               REX01-10G   8.5            7.527                                              REX01-10G   5.9            8.09                                               REX01-10G   10.1           6.963                                              REX02-24G   31.2           31.863                                             REX02-24G   31.3           32.036                                             REX02-24G   31             29.426                                             REX02-24G   29.1           30.14                                              REX02-24G   27.8           27.692                                             REX01-8A    1.9            3.391                                              REX01-8A    1.8            2.583                                              REX01-8A    2.0            1.411                                              REX01-8B    11.2           11.94                                              REX01-8B    11.4           8.105                                              REX01-8B    11.6           14.725                                             REX02-23A   27.4           25.109                                             REX02-23A   28.1           27.568                                             REX02-23A   28.7           28.394                                             REX01-8C    1.5            1.587                                              REX01-8C    1.7            2.125                                              REX01-8C    1.9            2.572                                              REX01-8D    5.8            3.81                                               REX01-8D    5.3            3.302                                              REX01-8D    6.4            7.352                                              ______________________________________                                    

A graph of the gravimetric gel measurements versus NIR generated gelmeasurements of the data of Table 2 is shown in FIG. 4. A correlationfactor of 0.98 was calculated along with a standard error of 1.7%. Thecurve for the regression is as follows:

    Y=0.988X+0.015 R.sup.2 =0.98

    Std. Error=1.7%

To further validate this model, gravimetric gel measurements and NIRgenerated gel measurements were taken on fifty consecutive samples oftoner. The mean and standard deviation of these samples are shown inTable 2 as follows:

                  TABLE 2                                                         ______________________________________                                                     CAA Measured                                                                             NIR Measured                                                       Gel Content                                                                              Gel Content                                           Extruder     (% Gel     (% Gel)                                               ______________________________________                                        ZSK-40       29.78 ± 1.30                                                                          29.19 ± 0.91                                       ZSK-58       24.62 ± 1.68                                                                          23.88 ± 1.27                                       ______________________________________                                    

The standard deviation for the NIR generated gel measurements is thusless than the standard deviation for the gravimetric gel measurements.The NIR measurements thus were more accurate.

Using a near infrared spectrophotometer with probe installed in the diehead of the extruder, the degree of cross-linking, or gel content couldbe quantified in a one minute analysis period. This measurement of gelcontent by NIR also provides the parameter needed for closed-loopfeedback control of the cross-linking reaction.

Referring first to FIG. 1, a toner preparing apparatus 20 in the form ofan extruding system is shown. The toner preparing apparatus 20 includesan extruder 22 for mixing chemical initiator 24 with dry resin 26 andfor converting the dry resin 24 into a liquid form having a portion ofthe toner in gel form. Generally, any extruder, such as a single or twinscrew extruder, suitable for preparing electrophotographic toners, maybe employed for mixing the chemical initiator 24 with the resin 26. Forexample a Werner & Pfleiderer WP-28 extruder is well-suited formelt-blending the resin 26, a chemical initiator 24, and additives. Theresin 26 is stored adjacent the extruder 22 in a dry toner resin feederhopper 62. The resin 26 is uniformly fed from the hopper 62 by an auger64 to a resin hopper outlet 66. The resin hopper outlet 66 is locatedadjacent a extruder resin inlet 70 into which the resin 26 is deposited.After the resin 26 is added to the extruder 22, the chemical initiator24 is added to the extruder 22. The chemical initiator may be wet ordry. The use of dry initiator will be described herein, but it should beappreciated that the chemical initiator may likewise be in liquid form.

The chemical initiator 24 may be any suitable chemical capable ofassisting the conversion of an unsaturated toner resin into a partiallysaturated toner resin. The percentage of conversion preferred may verywidely from approximately 40 percent for black toners to approximately5-7 percent for colored toners. An organic peroxide has been found to beeffective in assisting such a conversion from unsaturated toner resin topartially saturated toner resin. The organic peroxide for example may bea benzoyl peroxide.

The chemical initiator 24 is stored adjacent the extruder 22 in a drychemical initiator feeder hopper 63. The chemical initiator 24 isuniformly fed from the hopper 63 by an auger 65 to a chemical initiatoroutlet 67. The chemical initiator outlet 67 is located adjacent theextruder resin inlet 70 into which the chemical initiator 24 isdeposited. As the chemical initiator 24 is mixed with resin 26, anextrudate 110 is formed which contains the chemical initiator 24 evenlydistributed within the resin 26. The screws (not shown) within theextruder 22 are preferably turned at the fastest rate which allows themolten resin to achieve the desired temperatures. The extrudatecontinues to pass through the extruder 22 to a die plate 120 located atan outlet 122 of the extruder 22. The die plate 120 includes a largerectangular aperture 124 through which the extrudate 110 exits theextruder 22. At the die plate 120, the temperature is raised fromapproximately 110° C. to above 200° C. temperature to obtain atemperature which fluidizes the extrudate and causes it to flow freelythrough the aperture 124. The pressure in the preceding mixing zone canbe increased by restricting the size of the aperture 124, at the expenseof throughput. The aperture 124 is chosen of suitable size to provideflow sufficient to provide for a commercially acceptable process.

A detector such as a near-infrared (NIR) spectrophotometric sensor 130is located in the die plate 124. The near-infrared sensor 130 measuresthe % transmission of light through the resin at various wavelengths.Signals indicative of the % transmission of light at the variouswavelengths are sent by conduit 134, such as a fiber optic cable, to aNIR micro-processor 132. A typical fiber optic cable has a co-axialconstruction with an internal path to the NIR micro-processor and anexternal path to the sensor.

This results in a near infrared spectrum being created for the samplematerial. Then, based on the PLS regression of specific wavelengthintensities to gel content, as measured by the laboratory gravimetricmethod, the NIR micro-processor 132 predicts a gel content value for thesample. The NIR micro-processor 132 then converts the gel content to anelectrical signal which is sent via insulated copper wires 136 to thefeedback controller 135. The controller 135 may be any suitable devicecapable of comparing the signals from the NIR micro-processor 132 withthe desired value, or setpoint. For example, the controller 135 may be aprogrammable logic controller (PLC) or distributive control system (DCS)capable of proportional, integral, or derivative control (PID). Thefeedback controller 135 further compares the measured percent gelcontent in the resin sample to a predetermined desired percent gelcontent determined and entered by the operator. The controller 135 thencalculates a new ratio of initiator to resin and sends electricalsignals through conduits 137 and 138 respectively to control devices 139and 149, for example motors, to rotate the feed screws 64 and 65, forthe resin 26 and the initiator 24, respectively. The initiatorconcentration entering the extruder 22 is thus increased or decreased.For a modern production process, the extrudate passes through theextruder 22 in a matter of a few seconds. Therefore, the near-infraredsensor 130 can measure the gel content of the extrudate 110 and make animmediate adjustment in the chemical initiator 24 entering the extruder22 whereby only a minute amount of extrudate 110 will pass through theextruder 22 before the adjustment is made. It should be appreciated thatthe feedback controller 132 may include logic with a time delay (notshown) whereby the gel content of the extrudate 110 is measured by theinfra-red sensor 130 only at periodic intervals whereby the feedbacksystem may remain stable.

The control logic is shown schematically in FIG. 3. At operational block150 resin is added to the extruder 22 by feeder 64. Next, at operationalblock 152, the chemical initiator is added by feeder 65. Next, atoperational block 154, the chemical initiator 24 is mixed with the resin26 in the extruder 22. At operational block 156, the near-infraredsensor 130 measures the percent gel content. At decision block 160 themeasured gel content is compared with the desired gel content within thelogic of the feedback controller 132. If the measured gel content of theextrudate 110 is the same or almost the same as the desired gel contentof the extrudate 110, the extruder 22 continues to operate with thefeeder 65 remaining at its present rate and the gel contented toner isremoved in operational block 162 for further processing.

Alternatively, if the measured gel content of the extrudate 110 isdifferent than the desired gel content of the extrudate 110, adetermination is made at decision block 164 whether the gel contentsignal of the extrudate 110 is too low or too high. If the gel contentsignal is too low, the ratio of feeder 64 rate to feeder 65 rate isdecreased at operational block 166, such that a constant totalthroughput is maintained (feeder 64 rate+feeder 65 rate=constant).Likewise, if the gel content signal is too high, the ratio of feeder 64rate to feeder 65 rate is increased at operational block 170.

The chemical initiator 24 which now has a revised flow rate is thenmixed with resin 26 which also has a revised flow rate as shown inoperational block 154. As shown in operational block 156, the gelcontent of the extrudate 110 is measured by the infra-red sensor 130and, then as shown in decisional block 160, the measured gel content ofthe extrudate 110 is compared with the desired gel content of theextrudate 110. If the gel content is not the same, the decisional block164 is reached and further adjustment of the feeder 64 to feeder 65 rateratio is made, whereas if the gel content is the same, the operationalblock 162 is reached and the resin is removed for further processing.

The extrudate 110 from the extruder 22 is further processed into smallparticles by a mill or other commercially available equipment.

The extrudate 110 may be used as a resin to be inputted into a tonerextruder where it may be blended with additives and colorant to form atoner or, alternatively, the resin 26 may possibly be blended withadditives and colorant simultaneously with the addition of chemicalinitiator to provide an extrudate 110 in the form of a toner.

The use of the NIR spectrophotometric gel content feedback system of thepresent invention provides for real time chemical initiator leveladjustment with the ability to fine tune the gel content of the resin ortoner produced. When the wet chemical gravimetric analysis is usedeither the system must be shut down for at least 36 hours or the systemmay be producing defective toner for that period of time.

While the invention has been described with reference to the structuresand embodiments disclosed herein, it is not confined to the details setforth, and encompasses such modifications or changes as may come withinthe purpose of the invention.

We claim:
 1. A method for the preparation of modified resins includingcross-linked microgel particles from a mixture of resin particles and aninitiator, comprising:conveying the resin particles through an extruder;adding the initiator to the resin in the extruder to form the modifiedresin; measuring the cross-linked gel in the modified resinsubstantially immediately after mixing in the extruder; by transmittingfrom a spectroscope a signal indicative of the quantity of cross-linkagein the microgel resin.
 2. The method of claim 1, further comprisingconverting the signal indicative of the quantity of the cross-linked gelto an initiator signal indicative of the quantity of initiator in themodified resin.
 3. The method of claim 2, further comprising controllingthe addition rate of the initiator to the extruder in response to theinitiator signal.
 4. The method of claim 1, further comprisingconnecting initiator chambers to said extruder simultaneously with thestep of conveying the resin.
 5. The method of claim 2, furthercomprising determining that the quantity of cross-linked microgelparticles in the modified resin is within an acceptable quantity range.6. A method of claim 2, wherein the measuring step comprises:measuringspectral bands of the cross-linked gel in the modified resin; andconverting the spectral bands into a measurement of the quantity ofcross-linked gel.